Rasterization of very large triangles was causing signed 32-bit
integer overflow due to multiplying two unsigned 12.4 fixed-point
coordinates. The equations have been reworked to only require
multiplication of 12.4 by 0.4 fixed-point.

Bug b/34078120

Change-Id: I227b81254559af04baf50fbfec6a7f123bd230e3
Reviewed-on: https://swiftshader-review.googlesource.com/8370Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>